The success of rotary drilling enabled the discovery of deep oil and gas reservoirs. The rotary rock bit was an important invention that made rotary drilling economical.
In drilling boreholes in earthen formations by the rotary method, rock bits typically fitted with three rolling cutters are employed. The bit is secured to the lower end of a drill string that is rotated from the surface or by downhole motors or turbines. The cutters mounted on the bit roll and slide upon the bottom of the borehole as the drill string is rotated, thereby engaging and disintegrating the formation material to be removed. The roller cutters are provided with teeth or cutting elements that are forced to penetrate and gouge the bottom of the borehole by weight from the drill string. The cuttings from the bottom and sidewalls of the borehole are washed away by drilling fluid that is pumped down from the surface through the hollow, rotating drill string and are carried in suspension in the drilling fluid to the surface.
It has been a conventional practice for several years to provide diamond or super-hard cutting elements or inserts in earth-boring bits known as PDC, or fixed cutter bits. The excellent hardness, wear, and heat dissipation characteristics of diamond and other super-hard materials are of particular benefit in fixed cutter or drag bits, in which the primary cutting mechanism is scraping. Diamond cutting elements in fixed cutter or drag bits commonly comprise a disk or table of natural or polycrystalline diamond integrally formed on a cemented tungsten carbide or similar hard metal substrate in the form of a stud or cylindrical body that is subsequently brazed or mechanically fit on a bit body.
Implementation of diamond cutting elements as the primary cutting structure in earth-boring bits of the rolling cutter variety has been somewhat less common than with earth boring bits of the fixed cutter variety. In the rolling cutter variety, generally a diamond cap is formed on a cylindrical tungsten carbide base. The cap may be conical, hemispherical, or other shapes. While successful, improvements in wear resistance and penetration rate are desired.